It is necessary in many systems to bring a moveable member to a stop at a precise location. For example, in a magnetic memory disk device bearing a number of information and servo tracks, it is required that the read/write head be positioned over a particular track. Likewise, in a high speed printer with intermittent print wheel movement, it is required that the print wheel be rotated so that a particular character is in the print position.
Closed loop servo system, such as the system described in U.S. Pat. No. 3,663,880, utilize a signal indicative of the instantaneous velocity of the motor shaft supporting the member to be positioned. Accordingly, it is important that the velocity signal used for such positioning have an amplitude at all times directly proportional to the velocity of the supporting motor shaft.